The chips from whole trees and similar material provide an inexpensive source of fibre which many pulp mills are now using in varying proportions in combination with regular chips. Chips from whole trees generally contain significant amounts of long twigs or branches that cause costly handling problems, for example, hang up in chip bins, metering valves etc., and the use of these chips is therefore restricted.
Conventional V-drum chippers used to chip whole tree include a substantially cylindrical housing containing a V-drum rotor (formed by a pair of axially aligned substantially identical frustro-conical hollow disc having their smaller diameter ends connected together to form the rotor). Each of the discs of the rotor is provided with knives and slots therethrough adjacent the knives for passage of chips cut by the knives through the discs into chip chambers provided one at each end of the rotor. The chips are ejected from the chip chamber by suitable paddles formed at the larger diameter end of each of the discs. Twigs or branch stems or other debris that do not pass through the discs are directed into the chamber and ejected with the chips. No simple and effective means has been provided for separating this debris from the chips in the V-drum chipper.
The above identified Continuation-in-Part Application No. 855,073 discloses a disc type chipper wherein the chipper disc divides the housing into a front chamber and a rear chamber. In this arrangement the debris including the twigs and branches not chipped by the knives are moved into the front chamber and ejected through a debris outlet leading from the front chamber while the cut material (chips) passes through slots in the disc into a chip chamber and is ejected separately from the housing to a chip outlet.
It has also been proposed to separate dirt and loose bark in a drum chipper designed to chip short lengths of large diameter logs. In this chipper the short lengths are fed radially (longitudinal axis of the log and of the drum are aligned) and the knives cut substantially parallel to the grain of the wood to cut chips which pass into the drum. This device is totally unsuitable for chipping of whole trees.